Those with NSF (25). 40 subjects selected through Northwestern University Department of Dermatology's existing medical records and pathology specimens. Medical records will be reviewed to identify 10 subjects who have had a standard of care skin biopsy in the dermatology clinics at Northwestern University and who were exposed to Gadolinium in the 2 years prior to skin biopsy. Another 10 subjects who have had skin biopsy and who have never been exposed to GBCA during a medical imaging procedure will also be identified. Another 10 subjects on dialysis or with eGFR ≤30 exposed to GBCA in the 2 years prior to skin biopsy will be identified. Another group of 10 subjects on dialysis or with eGFR ≤30 who have had skin biopsy and who have never been exposed to GBCA during a medical imaging procedure will also be identified. Neonatal skin tissue of up to 10 subjects with existing skin tissue sample will be sent for analysis.